JPS63272131A - Polarization diversity optical reception method and device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method and device for obtaining stable reception characteristics against variations in the polarization state of an optical signal, and particularly to a method for simplifying the configuration of an optical receiving device, The present invention relates to a polarization diversity optical reception method and apparatus suitable for downsizing, cost reduction, and power consumption.

[Conventional technology]

Conventionally, regarding polarization diversity optical receivers, for example, "I.O.C.
C'83. June 27-30゜1983, Te
Chnical Digest pp, 386-38
7). FIG. 9 shows the basic configuration of the polarization diversity optical receiver discussed in the above literature.

In FIG. 9, 1 is a signal light and 4 is a reference light. 2a
, 2b are polarization separators that separate input light into two polarization components whose polarization planes are orthogonal to each other. 3a and 3b are separated signal lights, and their planes of polarization are orthogonal to each other. Similarly, reference lights 9a and 9b are separated, and their polarization planes are orthogonal to each other. 5a and 5b are mixers that match the planes of polarization of the signal lights 3a and 3b and the reference lights 9a and 9b, respectively, and mix them. 6a.

6b is mixed light. 10a and 10b are photodetectors, respectively, and lla and llb are their output signals. 1
A demodulator 2 obtains a demodulated signal 8 from the output signals 11a and llb. In the figure, since the signal lights 3a and 3b are two orthogonal polarization components of the signal light 1, the intensities of the signal lights 3a and 3b become zero at the same time for any polarization state of the signal light 1. It can't happen. Therefore output signal 1
It is impossible for the powers of 1a and llb to become zero at the same time, so it is impossible for the demodulated signal 8 to also become zero. As described above, the demodulated signal 8 is obtained for the signal light 1 in any polarization state.

[Problem that the invention seeks to solve]

The above conventional technology has the following problems.

1. A polarization separator is required to separate the reference light into two orthogonal polarization components, which increases the cost of the device.

2. Since the intensity of the reference light is attenuated during the process of the reference light passing through the polarization separator, it is necessary to increase the power consumption of the light source that outputs the reference light.

3. A part of the reference light is reflected by the polarization separator and returns to the light source that outputs the reference light, making the frequency of the reference light unstable.

4. Two mixers are required to obtain two mixed lights, increasing the cost of the device.

5. Two light receivers are required to accommodate the two mixed lights, and two sets of parts associated with the light receiving surface (optical lenses, electrical amplifiers, tt sources, etc.) are also required. Devices are becoming larger, have more complex configurations, higher costs, and higher power consumption. Furthermore, due to higher power consumption, the operating cost of the device increases and the amount of heat generated by the device also increases.

6. In order to make the characteristics of the two light receivers similar, it is necessary to select two light receivers with similar characteristics from a large number of light receivers, which increases the cost of the device.

7. As shown in FIG. 9, since the two reference beams cross, it is difficult to integrate the optical system into an optical integrated circuit, and it is not possible to reduce the cost and size of the device through integration.

An object of the present invention is to solve the above-mentioned problems, that is, to make the device smaller, simpler in structure, lower in cost and lower in power consumption, and to stabilize the reference frequency.

[Means for solving problems]

The above purpose is to separate the signal light into two polarized components whose planes of polarization are substantially orthogonal, mix the two separated beams with a reference beam so that their planes of polarization substantially match, and perform heterodyne detection or homodyne detection of the mixed light. This is achieved by obtaining a demodulated signal.

[Effect]

FIG. 1 shows the basic configuration of the present invention, and the present invention will be explained in detail using this diagram. In the same figure.

1 is a signal light. Reference numeral 2 denotes a polarization separator that separates the signal light 1 into two polarization components whose planes of polarization are substantially orthogonal. 3a and 3b are separated lights output from the polarization splitter 2, and their polarization planes are substantially orthogonal. 4 is a reference light and does not separate by 1 minute,
A mixer 5 mixes the separated beams 3a, 3b and the reference beam 4 so that their planes of polarization substantially match. 6 is mixed light output from the mixer 5. A detector 7 performs heterodyne detection or homodyne detection of the mixed light 6, and includes one photoreceiver. A demodulated signal 8 is obtained from the mixed light 6. The mixed light 6 includes the 1-separated lights 3a and 3b with their polarization planes substantially matching.Since the 6-separated lights 3a and 3b are originally two orthogonal polarization components of the signal light 1, no Even with respect to the polarization state, the intensity of the separated beams 3a and 3b will not be zero at the same time, so the intensity of the signal light included in the mixed light 6 will not be zero, and therefore the demodulated signal 8 will also be zero. In other words, the demodulated signal 8 is obtained for signal light of any polarization state. In particular, the separated lights 3a and 3 during mixing
The smaller the phase difference between b, the more efficiently a demodulated signal can be obtained.

[Example] FIG. 2 shows an example of the present invention. The figure shows signal light 1
is a binary ASK (amplitude shift keying) signal or a binary FSK (frequency shift keying) signal,
This is an example of the configuration of a receiving device for performing heterodyne optical detection of these signals. In the figure, 23 is an optical component having a function of separating signal light into orthogonal polarization components, and in this embodiment, a polarization beam splitter is used. 24 is a reflecting mirror.

This reflection 1lt24 is caused by the polarization controller 13 and the optical coupler 2.
This can be omitted by changing the location of 5.

As the optical coupler 25, for example, a single mode optical fiber type optical coupler can be used. 26 is a band pass filter. A detector 27 outputs the output signal of the filter 26 as a baseband signal, and in this embodiment, an envelope detector is used.

As the polarization plane controller 13, for example, a half wavelength plate can be used. The photodetector 16 can be a pin photo diode (PIN-PD) or an avalanche photodiode (PIN-PD).
A photodiode (APD) can be used.

The operating principle of FIG. 2 will now be explained.

The signal light 1 is separated into two orthogonal polarization components by the polarization beam splitter 23. One component is output as is as separated light 3a. The other component is the reflector 24
After being reflected by the beam, it is output as separated light 3b. The plane of polarization of the separated light 3b is rotated by 90 degrees in the polarization plane controller 13, and the plane of polarization matches that of the separated light 3a. Separated light 3a
The output lights from the polarization plane controller 13 and the polarization plane controller 13 are inputted to the optical coupler 25 from different input ends. At this time, when the polarization plane of the reference beam 4 is input into the optical coupler 25 with the polarization plane of the reference beam 4 matched with the polarization plane of the separated beam 3a in advance, the polarization planes of the three types of lights (output lights 3a, 13 and 4) are matched. mixed in state, mixed light 6
is output from the optical coupler 25. The mixed light 6 is input to a photoreceiver 16 and subjected to heterodyne optical detection. Here, if the signal light 1 is a binary ASK signal, all signal components output from the light receiver 16 pass through the bandpass filter 26. However, when the signal light 1 is a binary FSK signal, either the space signal component or the space signal component in the signal output from the light receiver 16 passes through the bandpass filter 26. As a result, the filter 26 outputs an electrical binary ASK signal. The output signal of the filter 26 is converted into a baseband signal by an envelope detector 27 and output as a demodulated signal 8. After the signal light 1 is separated into two orthogonal polarization components.

The respective planes of polarization are mixed with the reference light so that they match the plane of polarization of the reference light, and input to the light receiver 16 .

Therefore, the demodulated signal 8 can be obtained for the signal light 1 in any polarization state.

According to this embodiment, it is possible to realize an apparatus with a simple configuration.

FIG. 3 shows an embodiment of the mixer 5 of the present invention.

The mixer 5 can be realized by arbitrarily combining the function of controlling the plane of polarization of light and the function of combining two or three lights.

The function of controlling the plane of polarization of light can be achieved using birefringent crystals (for example, a half-wave plate, etc.), magneto-optic crystals (for example, a half-wave plate, etc.).

The applied magnetic field may be variable or fixed, such as an isolator) or an optical waveguide (single-mode optical fiber, polarization-maintaining optical fiber, etc.), or an integrated guided waveguide in which the optical fiber may be twisted. The material is SiO
It can be realized by using a wide variety of materials including x, LiNb0z (lithium niobate), and integration can be either hybrid or monolithic.

The function of combining light is a single mode optical fiber coupler,
This can be realized using a polarization maintaining optical fiber type coupler, a directional coupler type coupler, an integrated optical waveguide type coupler, or the like.

In FIG. 3, 13 indicates a polarization controller, and 14 indicates a multiplexer.

FIG. 3(a) shows an example in which a mixer is constructed using one polarization controller and one multiplexer. In the figure, the polarization plane of the one-separated light 3a is changed to approximately 9 by the polarization plane controller 13.
It is tilted by 0 degrees, and its plane of polarization is approximately parallel to the plane of polarization of the separated light 3b. The output light of the polarization controller 13, the separated light 3b, and the reference light 4 are combined in a multiplexer 14 with their polarization planes substantially matching, and are output as mixed light 6. Reference light 4 is.

The light is input to the multiplexer 14 with its plane of polarization substantially parallel to the plane of polarization of the separated light 3b. Such a situation is 1.For example, reference light 4.
It is a light source that outputs . The pn junction surface of the semiconductor laser is
The polarized light is polarized by making it substantially parallel to the polarization plane of the separated light 3b, or by inputting the output light of the light emitting element into a polarizing plate or the like so that the polarization plane of the output light is substantially parallel to the polarization plane of the separated light 3b. This can be realized by adjusting the angle of the plate and using the output light of the polarizing plate as the reference light 4.

According to the embodiment shown in FIG. 3(a), the mixer can be realized using one polarization controller and one multiplexer, so the mixer can be realized in a small size, with a simple configuration, and at low cost. Get the effect of being able to do it.

In FIG. 3(b), separated beams 3a and 3b are combined with their polarization planes substantially parallel, and the combined beam is combined with a reference beam 4 whose polarization planes are substantially the same.
An example of the configuration of a mixer in the case where the mixed light 6 is obtained by combining the two is shown. According to this configuration example, since the multiplexing of the separated lights 3a and 3b and the multiplexing of the multiplexed light and the reference light are performed using different multiplexers, the location of the multiplexers 14a and 14b can be freely selected. Get the effect of being able to do something. The multiplexed light output from the multiplexer 14a can also be guided using an optical waveguide or the like that preserves the plane of polarization and input to the multiplexer 14b.

In FIG. 3(c), the separated light 3b and the reference light 4 are combined with their polarization planes being substantially parallel, and the polarization plane of the combined light is controlled to be substantially parallel to the polarization plane of the separated light 3a. According to the one-piece configuration example showing the configuration example of the mixer that combines the multiplexers 14c and 14d with the multiplexers 14c and 14d, it is possible to freely select the arrangement location of the multiplexers 14c and 14d.

FIG. 4 shows a second embodiment of the mixer of the invention. In this embodiment, in the first embodiment of the mixer, the phases of the two separated lights 3a and 3b are controlled so that the two separated lights 3a and 3b are included in the mixed light 6 with their phases substantially matching. This is an example of the configuration of a mixer when In the figure, 13 is a polarization controller, 14 is a multiplexer, and 15 is a phase controller.1 Phase controller 15 is an electro-optic crystal that can control the refractive index by applied voltage, or can control the refractive index by injection current. This can be realized using a semiconductor phase controller or the like that can be used.

FIG. 4(a) shows an example of the configuration of a mixer in which the phase of the separated light 3a is controlled before the polarization plane is controlled by the polarization plane controller 13. FIG. 6B shows an example in which the polarization plane of the single-separated light 3a is controlled by 13, and then the phase is controlled. FIG. 4C shows an example in which the phases of both separated beams 3a and 3b are controlled.

Note that even in configurations other than those shown in FIGS. 4(a) to (Q), at least the phase controller may be placed anywhere as long as the phases of 3a and 3b included in the mixed light 6 substantially match. Furthermore, the configurations of the polarization controller and the multiplexer are similar to those of the first embodiment of the mixer.

According to this embodiment, since the two separated lights are included in the mixed light in a state in which the phases substantially match, the detection efficiency can be increased.

FIG. 5 shows an embodiment of the detector of the present invention.

In the figure, 6 is mixed light, 7 is a detector, and 8 is a demodulated signal. Further, 16 is a light receiver, which includes a PIN-PD (pin photo diode) which is a semiconductor light receiving element, and an AP
This can be realized using a D (avalanche photodiode) or the like. FIG. 5(a) shows an example of the configuration of a homodyne detector. At this time.

The frequencies of the signal light (combined light of 3a and 3b) included in the mixed light 6 and the reference light are substantially the same. Further, when the mixed light 6 is input to the light receiver 16, the detection efficiency is high when the signal light and the reference light have substantially the same phase.

A baseband signal is obtained as the electrical signal output of 16. This baseband signal becomes the demodulated signal 8.

FIG. 2B shows an example of the configuration of a heterodyne detector. At this time, the frequencies of the signal light (combined light of 3a and 3b) included in the mixed light 6 and the reference light are different.

When the mixed light 6 is input to the light receiver 16, an intermediate frequency signal 17 is obtained as an electrical signal output of the light receiver 16. 18 is a detector that converts 17 into a baseband signal. This detector 1
8 can be realized using an envelope detector, a delayed detector, or a synchronous detector. The output baseband signal becomes a demodulated signal.

According to this embodiment, it is possible to realize a detector with a simple configuration.

Incidentally, FIG. 6 shows an embodiment in which the electrical signal of the embodiment of FIG. 5 is amplified by an amplifier. In the figure, 19 is an amplifier. FIG. 6(a) shows an example of a homodyne detector in which the electrical signal output of the light receiver 16 is amplified. FIG. 2B shows an example in which the intermediate frequency signal 17 is amplified in a heterodyne detector. Same figure (Q)
teeth.

This is an example of a case where both the electrical signal output of the detector 18 and the detector 17 are amplified in a heterodyne detector.

There may also be a configuration example in which the amplifier 19a is omitted in contrast to FIG. 3(c). As shown in FIG. 6, when an amplifier is used, there is also the advantage that the magnitude of the demodulated signal can be controlled arbitrarily.

FIG. 7 shows a third embodiment of the mixer of the present invention. In this embodiment, in the first and second embodiments of the mixer,
This is an example of the configuration of a mixer when the intensity of reference light is controlled so that the average power of the demodulated signal is approximately constant. In the figure, 20 is an intensity controller for controlling light intensity, which can be realized by a light intensity modulator using an electro-optic crystal or a semiconductor.

21 is the mixer shown in the first and second embodiments of the mixer. The power of the demodulated signal can be detected by partially branching the demodulated signal and measuring the power of one branch signal. The intensity of the reference light can also be controlled by controlling the light output of the light source itself that outputs the reference light 4.

However, as shown in FIGS. 7(a) and 7(b), it can also be realized by keeping the light output 4 of the light source constant and controlling the intensity of the light output by 2o. The figure (b) is
This is an example in which the intensity of the reference light is controlled by 20 and the phase is further controlled by 15, and is suitable when the detector is a homodyne detector.

According to this embodiment, it is possible to obtain a demodulated signal with stable power regardless of the average intensity fluctuation and polarization state fluctuation of the signal light.

FIG. 8 shows an embodiment relating to optical waveguide of the present invention.

In this embodiment, at least one of the separated beams 3a, 3b, the reference beam 4, and the mixed beam 6 is guided through an optical waveguide that preserves the polarization state. It is an optical waveguide that preserves polarization, and can be realized using, for example, a polarization-maintaining optical fiber. FIG. 8(a) shows an example in which separated beams 3a and 3b are guided by optical waveguides 22a and 22b, respectively, and FIG. This is an example of waveguide at 22C.

Even in configurations other than those shown in Figures (a) and (b), J a H3b,
Any configuration is sufficient as long as at least one of 4 and 6 is guided by 22.

According to this embodiment, it is possible to freely select the arrangement of the polarization separator, mixer, and detector in the optical receiver.

〔Effect of the invention〕

According to the present invention, the following effects are obtained.

1. Since the reference light is mixed with the signal light without being separated, there is no need for a polarization splitter for separating the reference light, which was required in the past, and the cost of the device can be reduced.

2. Since the reference light is mixed with the signal light without passing through a polarization splitter, there is no attenuation that the intensity of the reference target suffers in the past, and the power consumption of the light source that outputs the reference light can be reduced.

3. Since the reference light is mixed with the signal light without passing through the polarization splitter, there is no reflected light returning from the polarization splitter to the light source, which existed in the past, and the frequency of the reference light can be stabilized.

4. The number of mixed lights to be obtained is one, so the number of mixers that were conventionally required to be two can be halved, and the cost of the device can be reduced.

5. There is only one mixed light, which reduces the number of two receivers and two sets of parts associated with them (lenses, amplifiers, power supplies, etc.) required for conventional detectors, making the device more compact. transformation,
The configuration can be simplified, costs can be reduced, and power consumption can be reduced. Furthermore, by reducing power consumption, it is possible to reduce operating costs and heat generation of the device.

6. The number of photoreceivers required is one, and there is no need to select photoreceivers, which was required in the past, and the cost of the device can be reduced.

7. Since the M light and the reference light do not cross each other, the optical system can be integrated into an optical integrated circuit, and integration can reduce the cost and size of the device.

8. Obtain a demodulated signal for signal light of any polarization state.

[Brief explanation of the drawing]

FIG. 1 is a basic configuration diagram of the present invention, FIG. 2 is a diagram showing an embodiment of the present invention, FIG. 3, FIG. 4, and FIG. 7 are diagrams showing an embodiment of the mixer of the present invention. 5 and 6 are diagrams showing an embodiment of the detector of the present invention, FIG. 8 is a diagram showing an embodiment of the leading wave of the present invention, and FIG. 9 is a diagram showing an example of the configuration of a conventional device. DESCRIPTION OF SYMBOLS 1... Signal light, 2... Polarization separator, 3... Separated light, 4... Reference light, 5... Mixer, 6... Mixed light,
7... Detector, 8... Demodulated signal, 9... Separated reference light, 10... Light receiver. 11... 10 output signals, 12... demodulator, 13...
... Polarization controller, 14... Multiplexer, 15... Phase controller, 16... Light receiving surface. Fig. 1 Chika 3 Fig.〈l7) /f ◇3 color transcription Fig. 4 (C) Fig. S ((1,) r-1111ko (←) Fig. 6 (C> lg Rihoki (Ku) (b) Figure 2 (α) tb)

Claims (1)

[Claims] 1. Separate the signal light into two polarized components whose planes of polarization are substantially orthogonal, mix the two separated beams and a reference beam so that their planes of polarization substantially match, and generate the mixed light. A polarization diversity optical reception method characterized by obtaining a demodulated signal by heterodyne detection or homodyne detection. 2. A means for separating the signal light into two polarized components whose planes of polarization are substantially orthogonal, a means for mixing the two separated beams and a reference beam so that their planes of polarization substantially match, and a means for heterodyning the mixed light. 1. A polarization diversity optical receiver comprising means for performing wave detection or homodyne detection to obtain a demodulated signal.